.nav_container{
    text-align:center;
}

.nav_button{
    display:inline-block;
}

.nav_left{
    margin-right:1em;
}

.nav_center{
    margin-left:1em;
    margin-right:1em;
}

.nav_right{
    margin-left:1em;
}

@media screen and (min-width: 620px) {
    .centerize{
        -webkit-box-sizing: border-box;
        -moz-box-sizing: border-box;
        -o-box-sizing: border-box;
        -ms-box-sizing: border-box;
        box-sizing: border-box;
        position:absolute;
        left:50%;
        height:100%;
        width:600px;
        margin-left:-300px;
    }
}